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WO1993008477A1 - DETECTEUR DE pH AUTODIAGNOSTIQUE - Google Patents

DETECTEUR DE pH AUTODIAGNOSTIQUE Download PDF

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Publication number
WO1993008477A1
WO1993008477A1 PCT/US1992/008799 US9208799W WO9308477A1 WO 1993008477 A1 WO1993008477 A1 WO 1993008477A1 US 9208799 W US9208799 W US 9208799W WO 9308477 A1 WO9308477 A1 WO 9308477A1
Authority
WO
WIPO (PCT)
Prior art keywords
impedance
output
electrode
signal
time
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/US1992/008799
Other languages
English (en)
Inventor
Timothy J. Forsythe
Roland H. Koluvek
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Rosemount Inc
Original Assignee
Rosemount Analytical Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Rosemount Analytical Inc filed Critical Rosemount Analytical Inc
Priority to JP5507798A priority Critical patent/JPH07500419A/ja
Priority to CA002119435A priority patent/CA2119435C/fr
Priority to EP92922173A priority patent/EP0609334B1/fr
Priority to DE69223640T priority patent/DE69223640T2/de
Publication of WO1993008477A1 publication Critical patent/WO1993008477A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/28—Testing of electronic circuits, e.g. by signal tracer
    • G01R31/282—Testing of electronic circuits specially adapted for particular applications not provided for elsewhere
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/416—Systems
    • G01N27/4163—Systems checking the operation of, or calibrating, the measuring apparatus
    • G01N27/4165—Systems checking the operation of, or calibrating, the measuring apparatus for pH meters

Definitions

  • This invention relates to an amplifier circuit for use with a sensor which requires only three wires for connection to a remote circuit.
  • this invention allows for continuous process output measurement and continuous on line diagnosis of electrodes.
  • system of Patent No. 4,829,253, issued May 9, 1989 are capable of determining unknown values such as a voltage representation of the pH of a liquid and also of diagnosing electrode problems by checking the impedance of the sensor.
  • the present invention allows for continuous on line measurement of both the process measurement and impedance.
  • the method used to determine sensor impedance in the prior art is also not as reliable or as accurate as the present invention's method.
  • Prior art measures the decay time of the process output signal, or direct
  • the present invention provides a three wire amplifier circuit for use with a condition sensor, such as a pH sensor, to transmit to a remote circuit without using additional biasing circuitry.
  • the pre-amplifier of the present system is compact and easily fitted into an electrochemical probe.
  • the invention continuously measures a voltage representative of the on line process measurement and at the same time monitors sensor impedance using a square wave.
  • the square wave is inputted to a remote circuit, and transmitted to a pH sensor probe over one of three wires.
  • the other- two wires carry the ,l common ,, output of the system, and the voltage output of the preamplifier.
  • the output is converted into a pulse width modulated signal by an inverter and sampled. The sampled values are used to calculate process output and impedance.
  • Figure 1 is a schematic diagram of the three wire amplifier in combination with a pH sensing probe and an energization circuit
  • Figure 2 is a schematic representation of a wave form obtained.
  • FIG. 3 is a simplified flow chart which illustrates the determination of unwanted impedance change in an electrode.
  • a transmitter 10 is shown in dashed lines containing a pH probe 12 which includes a pH electrode 13 comprising a glass container- or cell 14 containing a known liquid 15 into which a conductor 16 is inserted and an electrode 18 which is inserted into a process fluid 20 whose pH is to be measured in a container 22.
  • Process fluid also contains a temperature probe 17.
  • Electrode 18 is shown only schematically and normally includes a salt bridge as is known in the art. These probes operate to develop a voltage e s between the conductor 16 and the electrode 18 which varies as a function of the pH of the liquid 20.
  • Electrode 18 is shown connected to a line 19 identified by the letter “C” which constitutes the "common” output of the system and is one of the three wires to the transmitter 10.
  • Conductor 16 is used for providing the output signals to the circuit and is connected to a junction point 38.
  • the resistance of the pH electrode 13 is represented by R s . This value will change when the glass cell becomes coated, cracked, or broken.
  • An amplifier 30 which is, for example, an operational amplifier of the type TLC 271A made by Texas Instruments is shown in the figure and has a high impedance, non-inverting or positive input 32 and an inverting or negative input 34.
  • the non-inverting input 32 is shown connected through a resistor 36 to the junction point 38 to which the conductor 16 is also connected.
  • the signal from the conductor 16 is thus coupled through resistor 36 to the non-inverting input of amplifier 30.
  • Resistor 36 in the preferred embodiment has a resistance of approximately 10K ohms. It is seen that the signal from conductor 16, which is related to the unknown voltage e B is presented to the non-inverting input of the operational amplifier 30.
  • a capacitor 39 is shown connected between the non- inverting input 32 and the offset terminal 40 for purpose of providing of bypass and amplifier stability, as shown.
  • a positive supply terminal 44 and a bias select terminal 46 are connected together to a conductor 50 which is identified by the letter "A" conductor 50, is the conductor for the positive side of the power supply to the system and is another of the three wires to the transmitter 10.
  • Conductor 50 is also connected through a capacitor 52 to the junction point 38 for purposes of providing a square wave - for use in checking the electrode 13 as will be described hereinafter.
  • capacitor 52 is approximately 1 nanofarad.
  • the transmitter 10 operates as a pre- amplifier and is usually mounted as close to the electrode 13 as possible. In use, the electrode 13, electrode 18, and the preamplifier all are mounted on a signal probe package 12, with the transmitter mounted at the head of the probe. The output of amplifier 30 is on a conductor
  • the transmitter 10 is usually located right on the probe 12, remote from the source of power and further signal conditioning circuits. Conductors which . supply the power supply inputs and the output are shown by the broken line connectors "A", "B", and "C", which lead from the transmitter 10 to a remote circuit 70..
  • Remote circuit 70 comprises an integrator 72 connected to an analog to digital converter 74, which is coupled to a microprocessor (CPU) 76.
  • the CPU 76 is connected to a MOSFET 78, and a RTD signal conditioner 80.
  • the integrator 72 is connected to a power supply 82.
  • the MOSFET 78 is coupled to a voltage divider network 84, 86 at its source 88, conductor C at its drain 90, and the CPU 76 at its gate 92.
  • Conductor B is connected directly to the integrator 72, which is connected to the analog to digital converter 74.
  • the RTD signal conditioner 80 is connected to a temperature probe 17 in the liquid 20, and is coupled to the CPU 76.
  • the CPU also provides a process output on line 94, impedance output on line 96, and error or fault signals on line 98.
  • a square wave is applied from the CPU 76 to the gate 92 of the MOSFET 78 resulting in a step voltage through the capacitor 52 and onto the process electrode's output on conductor 16.
  • a nonpolarized electrode may be maintained resulting in no interference of the electrodes average output.
  • a near perfectly symmetrical square wave of positive and negative pulses is maintained by using the voltage divider network 84, 86. This near perfect symmetry allows the ability to sample the- electrode 13 output and use this sample to obtain both sensor impedance and process output readings, by calculation methods described hereinafter.
  • T - measurement period t time variable
  • the process output is obtained by determining the ratio of the on-time to the total-time of the positive and negative pulses of the pulse width modulated signal from the integrator, and averaging them. Due to the symmetry of the pulses, the average of these ratios is the DC baseline equivalent to the process output.
  • the impedance output is obtained similarly, but by subtracting the two ratios and averaging them. This removes the DC baseline offset and leaves a signal indicating only the area under the decay curve, which in turn provides an accurate indication of impedance as indicated above.
  • Very large impedances have very long decay times.
  • the period of the square wave may not be long enough to allow the output to decay to its prestep value (DC baseline in Figure 2) before the next step occurs. This leads to errors in the impedance readings.
  • the readings can be corrected by capturing the voltage level when the last area segment is sampled (E ⁇ .) and using the basic formula above.
  • the impedance is further corrected for temperature errors by the following formula:
  • P c and Z c and the offsets from zero are derived factors determined from standard calibration procedures.
  • the procedure for determining the quantity is the same for both process output calibration and impedance calibration.
  • the calibrator inputs both a low and a high process value, and records in the computer the "actual" values inputted from the output signal.
  • the high and low actual values (A) and the high and low measured values (M) are then used to calculate the span and offset values for the process.
  • the process calculations are shown below.
  • the impedance calculations are identical:
  • a cracked electrode is indicated by a sharp decrease in electrode impedance.
  • the user enters a set point impedance value equivalent to the amount of error (decrease in impedance) to be allowed in percentage, which would indicate a cracked electrode.
  • This method works by using the following filtering equation with two different values for the filter constant.
  • the filter values are functions of time, which represent response time by the system. By using two different values of the filter constant, a trend of the upward or downward shifts of impedances is maintained.
  • the larger filter constant corresponds to a slower response of the system, where the smaller filter constant corresponds to a faster response time.
  • Z f (fast) with the faster or smaller filter constant will change faster than Z f (slow) with the large or slow filter constant. If the difference between the two values of -Z f exceeds a predefined value, 10% for example, a timer is started, and the value of Z f (slow) with the larger filter constant is stored for reference. At some user defined period of time later, the difference between Z f (fast) with small filter constant and Z f (slow) that was stored is calculated. If this difference value exceeds a user preset value of error, it is known a cracked electrode exists, and an error signal is generated. The timer is used to prevent a stray noise signal from generating an error. By comparing Z s (fast) and the same Z f (slow) , at some period of time apart, the chances of stray noises causing faults are greatly reduced. This is illustrated by the flow chart of Figure 3.
  • the fault signal of Figure 3 which indicates an impedance variation, can be used to drive a display or to operate a relay to provide an alarm.
  • the fault signal can be set to be provided as a prediction of failure, to give an alarm, or indicate when an electrode should be replaced.
  • the signal can be to indicate when the electrode impedance exceeds a user selected value indicating an old or coated electrode, or when the impedance falls below a selected value indicating a cracked electrode.
  • Failed electrodes are indicated by either very high or very low impedances.
  • the procedure allows the user to enter maximum and minimum impedance values for fault purposes. If the impedance values exceed these limits, fault signals are generated. Coated andaging electrodes' impedances slowly rise over a period of time. This procedure stores the nominal impedance value each time a calibration is performed. The user enters a value equivalent to the amount of error in percentage before calibration is needed. These values may vary depending on the type of electrode and the process in which the electrode is immersed. When the value entered is reached, a fault indicator informs the user that replacement, maintenance and/or recalibration is necessary.
  • the apparatus is shown with a pH sensor, but can be adapted for indications of impedances of electrodes of general use chemical sensors such as sensors for sensing sodium or potassium.

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  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Molecular Biology (AREA)
  • General Engineering & Computer Science (AREA)
  • Engineering & Computer Science (AREA)
  • Electrochemistry (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
  • Measurement Of Resistance Or Impedance (AREA)

Abstract

Appareil et procédé permettant de mesurer l'impédance potentiométrique d'une électrode à des fins diagnostiques tout en pouvant lire en continu les résultats de la valeur traitée. Une onde carrée est appliquée à un circuit externe (78, 84) qui, à son tour, est couplé à une sortie d'un ensemble à électrodes (13), par l'intermédiaire d'un condensateur (52). La sortie de l'électrode (13) est convertie en un signal modulé en largeur d'impulsions et échantillonnée. Ces valeurs échantillonnées sont utilisées pour calculer l'impédance et la valeur de sortie du traitement.
PCT/US1992/008799 1991-10-25 1992-10-14 DETECTEUR DE pH AUTODIAGNOSTIQUE Ceased WO1993008477A1 (fr)

Priority Applications (4)

Application Number Priority Date Filing Date Title
JP5507798A JPH07500419A (ja) 1991-10-25 1992-10-14 自己診断機能付きｐＨセンサ
CA002119435A CA2119435C (fr) 1991-10-25 1992-10-14 Detecteur de ph a auto-diagnostic
EP92922173A EP0609334B1 (fr) 1991-10-25 1992-10-14 DETECTEUR DE pH AUTODIAGNOSTIQUE
DE69223640T DE69223640T2 (de) 1991-10-25 1992-10-14 Ph-sensor mit selbstdiagnose-funktion

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US781,312 1991-10-25
US07/781,312 US5268852A (en) 1991-10-25 1991-10-25 Self diagnostic pH sensor

Publications (1)

Publication Number Publication Date
WO1993008477A1 true WO1993008477A1 (fr) 1993-04-29

Family

ID=25122337

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US1992/008799 Ceased WO1993008477A1 (fr) 1991-10-25 1992-10-14 DETECTEUR DE pH AUTODIAGNOSTIQUE

Country Status (7)

Country Link
US (1) US5268852A (fr)
EP (1) EP0609334B1 (fr)
JP (1) JPH07500419A (fr)
CA (1) CA2119435C (fr)
DE (1) DE69223640T2 (fr)
RU (1) RU94021696A (fr)
WO (1) WO1993008477A1 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999018430A1 (fr) * 1997-10-06 1999-04-15 City Technology Limited Detecteurs electrochimiques
EP1143239A1 (fr) * 2000-04-04 2001-10-10 Metrohm Ag Procédé de surveillance de la qualité de capteurs de mesures électrochimiques et dispositif de mesure avec un capteur électrochimique
EP1772728A1 (fr) * 2005-10-05 2007-04-11 Roche Diagnostics GmbH Procédé et système destinés à la surveillance de capteurs électrochimiques
CN111220674A (zh) * 2020-01-16 2020-06-02 上海博取环境技术有限公司 一种ph传感器故障监测装置及其监测方法

Families Citing this family (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5502388A (en) * 1993-02-04 1996-03-26 Hoechst Aktiengesellschaft Method of measuring the pH value of a test solution with glass-electrode measuring cells and of simultaneously calibrating the measuring cells
US5832410A (en) * 1994-12-06 1998-11-03 Lin; Shengfu Method of using a computer to collect chemical signals directly
US5644501A (en) * 1994-12-06 1997-07-01 Lin; Shengfu Method of using a computer to collect chemical signals directly
US5980728A (en) * 1996-09-24 1999-11-09 Rosemont Analytical Inc. Diagnostic method and apparatus for solid electrolyte gas analyzer
US5970428A (en) * 1997-10-08 1999-10-19 Elsag International N.V. Ground loop detector circuit and method
US6617488B1 (en) * 1997-10-14 2003-09-09 Indicator Technologies, Inc. Method and apparatus for indicating the conditions in an absorbent article
AU5500499A (en) * 1998-09-09 2000-03-27 Cominco Ltd. Apparatus for monitoring the operability of an electrochemical sensor
IL135309A0 (en) * 2000-03-28 2001-05-20 Ortal Apert Three-dimensional optical memory
DE10119471A1 (de) * 2001-04-20 2002-10-31 Micronas Gmbh Verfahren und Zweidrahtsensor zur Messung einer physikalischen Größe
WO2003019165A2 (fr) * 2001-08-22 2003-03-06 Instrumentation Laboratory Company Systeme automatise servant a calibrer automatiquement et en continu des capteurs electrochimiques
US6894502B2 (en) 2001-12-14 2005-05-17 Rosemount Analytical Inc. pH sensor with internal solution ground
EP1610120B2 (fr) 2004-06-22 2015-10-07 Mettler-Toledo AG Sonde de mesure potentiométrique avec une couche externe comme électrode complémentaire
WO2008021546A2 (fr) * 2006-08-18 2008-02-21 Rosemount Analytical, Inc. Mesure de l'impédance d'une électrode de mesure du ph
US8436621B2 (en) * 2009-01-16 2013-05-07 Kyungpook National University Industry-Academic Corporation Foundation pH measurement system using glass pH sensor
EP3594671B1 (fr) * 2018-07-10 2022-09-07 ABB Schweiz AG Procédé permettant de surveiller la fonction de détection d'un capteur potentiométrique et ensemble de capteur potentiométrique correspondent
US20250216351A1 (en) * 2023-12-27 2025-07-03 Georg Fischer Signet Llc pH Sensor Measurement

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US4013899A (en) * 1976-03-26 1977-03-22 Honeywell Inc. Apparatus for converting a potential signal developed between two high impedance electrodes to a current signal and for transmitting this current signal to a remote location over a two wire transmission
US4777444A (en) * 1986-04-15 1988-10-11 Yokogawa Electric Corporation Method and apparatus for testing the integrity of an electrode in a potentiometric measuring electrode system
US4829253A (en) * 1987-06-03 1989-05-09 Rosemount Inc. Three wire amplifier circuit with diagnostic capabilities
US4998068A (en) * 1989-05-16 1991-03-05 In-Situ, Inc. Bias current control for providing accurate potentiometric measurements
US5046028A (en) * 1989-02-06 1991-09-03 Bryan Avron I System for calibrating, monitoring and reporting the status of a pH sensor

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US4546441A (en) * 1982-07-22 1985-10-08 John Burch Method and apparatus for time based measurement of impedance
US4536274A (en) * 1983-04-18 1985-08-20 Diamond Shamrock Chemicals Company pH and CO2 sensing device and method of making the same

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4013899A (en) * 1976-03-26 1977-03-22 Honeywell Inc. Apparatus for converting a potential signal developed between two high impedance electrodes to a current signal and for transmitting this current signal to a remote location over a two wire transmission
US4777444A (en) * 1986-04-15 1988-10-11 Yokogawa Electric Corporation Method and apparatus for testing the integrity of an electrode in a potentiometric measuring electrode system
US4829253A (en) * 1987-06-03 1989-05-09 Rosemount Inc. Three wire amplifier circuit with diagnostic capabilities
US5046028A (en) * 1989-02-06 1991-09-03 Bryan Avron I System for calibrating, monitoring and reporting the status of a pH sensor
US4998068A (en) * 1989-05-16 1991-03-05 In-Situ, Inc. Bias current control for providing accurate potentiometric measurements

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See also references of EP0609334A4 *

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999018430A1 (fr) * 1997-10-06 1999-04-15 City Technology Limited Detecteurs electrochimiques
EP1143239A1 (fr) * 2000-04-04 2001-10-10 Metrohm Ag Procédé de surveillance de la qualité de capteurs de mesures électrochimiques et dispositif de mesure avec un capteur électrochimique
EP1772728A1 (fr) * 2005-10-05 2007-04-11 Roche Diagnostics GmbH Procédé et système destinés à la surveillance de capteurs électrochimiques
US7429865B2 (en) 2005-10-05 2008-09-30 Roche Diagnostics Operations, Inc. Method and system for error checking an electrochemical sensor
US7626401B2 (en) 2005-10-05 2009-12-01 Roche Diagnostics Operations, Inc. Method and system for error checking an electrochemical sensor
CN111220674A (zh) * 2020-01-16 2020-06-02 上海博取环境技术有限公司 一种ph传感器故障监测装置及其监测方法

Also Published As

Publication number Publication date
JPH07500419A (ja) 1995-01-12
EP0609334B1 (fr) 1997-12-17
RU94021696A (ru) 1996-04-27
DE69223640T2 (de) 1998-07-02
EP0609334A4 (en) 1994-09-21
DE69223640D1 (de) 1998-01-29
US5268852A (en) 1993-12-07
CA2119435A1 (fr) 1993-04-29
EP0609334A1 (fr) 1994-08-10
CA2119435C (fr) 2001-05-01

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